#include <stdio.h>

int main()
{
	int m;
	float f,cost;
	printf("请输入您的月用电量\n");
	scanf("%d", &m);
	if(m>50){
		cost = 50*0.53+(m-50)*0.58;
	}else{
		cost = m*0.53;
	}
	printf("cost = %.2f\n", cost);
	return 0;
}